Plastic is a popular material used to make baby bottles and other infant care products that are both transparent and shatter resistant. Typically, baby bottles are sterilized prior to use by immersion in boiling water or by exposure to the steam of boiling water. Times of exposure are typically 5-20 minutes, but exposures for up to an hour, and even longer, are possible. Conventional bottles made using common clear plastic materials, such as poly(ethylene terephthalate) (“PET”), typically lose their shape during sterilization due to the low glass transition temperature (Tg) of these materials relative to boiling water. Thus, plastics with higher Tg values, such as bisphenol-A polycarbonate, amorphous polyamide, and polysulfone, are commonly used to fabricate baby bottles.
Most baby bottles are produced by blow molding, which restricts the materials used in baby bottles to high Tg plastic materials. Blow molding typically involves the injection molding of a preform in an injection mold, followed by pressurized-air inflation of this preform at a warm temperature in a blow mold. The bottle is then quenched below the Tg of the material by contact with the blow mold. This quenching after inflation, however, traps molecular orientation into the sidewalls of the bottle that can be released during boiling-water sterilization, causing the bottle to distort or shrink. In order to prevent shrinkage during boiling water sterilization, the Tg of plastics currently employed in the prior art to produce blow molded baby bottles is at least 30° C. above boiling water, that is, at least 130° C.
These high Tg materials also have certain deficiencies, such as cost, unfavorable consumer perception because of the presence of bisphenol A, insufficient chemical resistance, insufficient hydrolytic stability, etc, which can limit their use in these applications. Thus, there is a need in the industry for baby bottles produced from alternative plastic materials.